Wireless system design, e.g., 5G system design, focuses heavily on energy-efficiency both on the network and the User Equipment (UE) side. Extending battery life is an important objective for most types of wireless devices, from smartphones to IoT devices. Depending on usage scenarios, idle or active mode energy consumption may dominate the overall energy budget. Regardless of the individual UE product scenarios, the UE platform must ensure high energy efficiency in both operating modes to meet operator Key Performance Indicators (KPIs).
Selective transmissions, e.g., transmitting signals from a selected subset of antenna ports of a multi-antenna UE, provide one opportunity for reducing energy consumption for wireless devices. In multi-antenna UEs, multiple antenna ports may be defined for UE channel sounding. In a straightforward solution, for example, all the ports may be included in the sounding process to provide an Access Node (AN) with as much information as possible. In exemplary systems, transmissions from different antenna ports may be multiplexed in time, frequency, or using different time/frequency comb patterns. Some of the antenna ports in the UE may radiate energy towards the serving AN collecting the sounding information, while some others may not. Current discussions in 3GPP standards, e.g., 3GPP R1-1610151 “Views on RS for CSI acquisition,” RAN1 #86bis, 14 Oct. 2016, propose allocating Sounding Reference Signals (SRSs) transmission power on a limited number of “good” antenna ports, and omit transmitting SRSs over other antenna ports. For example, the “good” antenna ports may be identified or defined based on Down Link (DL) measurements of the individual antenna ports, dynamically allocated each subframe, and SRS transmissions may be omitted for antenna ports that contribute negligible energy or are unlikely to “reach” the serving AN. Such selective SRS transmission improves transmission power utilization and SRS coverage, and reduces interference in directions other than the target AN.
While the above-described selective SRS transmission reduces the overall transmission power of a device, and thus reduces power consumption, such selective transmission may not sufficiently address or reduce the power consumption of the device. For example, during subframes where certain antenna ports are not transmitting, RF chains of the respective antenna ports are generally still turned on and thus consume energy. Thus, the selective SRS transmission approach improves SRS power allocation and reduces interference, but UE energy efficiency remains suboptimal. Naïve approaches of always turning off transmission components of the RF chains coupled to the inactive antenna ports are not usable in many scenarios because the transient durations required to turning them back on again may be prohibitively long and thus may cause performance degradation. Thus, there remains a need for solutions that improve the battery efficiency of wireless devices.